The memory stages of a spatial Y-maze task are not affected by a low dose of ketamine/midazolam

Ketamine Administration Leads to Learning-Memory Dysfunction and Decreases Serum Brain-Derived Neurotrophic Factor in Rats

OBJECTIVE

This study investigated the effects of acute or chronic ketamine administration on learning and memory function as well as levels of brain-derived neurotrophic factor (BDNF) in the hippocampus and blood in order to explore the potential correlation between learning-memory dysfunction and ketamine.

METHODS

Rats were treated with 25 mg/kg ketamine for 3 d (n = 20) or 14 d (n = 20). Saline-treated rats were used as controls. The Morris water maze test was used to evaluate spatial learning and memory after 10 d of withdrawal. The level of BDNF in serum and the hippocampus were measured by ELISA.

RESULTS

The number of platform crossings and residence time in the target platform quadrant were significantly reduced in ketamine 3 d and 14 d groups than in the saline controls (both p < 0.05). In addition, the average escape latency of ketamine 3 d and 14 d groups were significantly longer than that of the saline 3 d and 14 d groups (p < 0.0001), respectively. Further examination found that only serum samples from ketamine 14 d group showed significantly decreased BDNF level compared to that from saline 14 d groups (p < 0.05). However, no differences were detected in hippocampus samples.

CONCLUSION

Chronic ketamine exposure (25 mg/kg) causes spatial learning and memory deficits in SD rats, which may be associated with decreased serum BDNF levels.

Administration of the benzodiazepine midazolam increases tau phosphorylation in the mouse brain

Preclinical studies have shown that anesthesia might accelerate the clinical progression of Alzheimer's disease (AD) and can have an impact on tau pathology, a hallmark of AD. Although benzodiazepines have been suggested to increase the risk of incident dementia, their impact on tau pathology in vivo is unknown. We thus examined the impact of midazolam, a benzodiazepine that is often administered perioperatively as an anxiolytic, on tau hyperphosphorylation in nontransgenic and in hTau mice, the latter a model of AD-like tau pathology. The acute administration of midazolam in C57BL/6 mice was associated with downregulation of protein phosphatase-1 and a significant and persistent increase in brain tau phosphorylation. In hTau mice, tau hyperphosphorylation was also observed; however, midazolam was neither associated with proaggregant changes nor spatial reference memory impairment. In C57BL/6 mice, chronic midazolam administration immediately increased hippocampal tau phosphorylation, and this effect was more pronounced in older mice. Interestingly, in young C57BL/6 mice, chronic midazolam administration induced hippocampal tau hyperphosphorylation, which persisted for 1 week. In hTau mice, chronic midazolam administration increased hippocampal tau phosphorylation and, although this was not associated with proaggregant changes, this correlated with a decreased capacity of tau to bind to preassembled microtubules. These findings suggest that midazolam can induce significant tau hyperphosphorylation in vivo, which persists well beyond recovery from its sedative effects. Moreover, it can disrupt one of tau's critical functions. Hence, future studies should focus on the impact of more prolonged or repeated benzodiazepine exposure on tau pathology and cognitive decline.

Ketamine alone or combined with midazolam or dexmedetomidine does not affect anxiety-like behaviours and memory in adult Wistar rats

Ketamine administration has been associated with controversial behavioural impairments and psychotic episodes. Even though ketamine alone and in combination with midazolam or dexmedetomidine are frequently used in laboratory animals, the side-effects of such protocols are not well known. Therefore, our aim was to evaluate the effects of ketamine alone and in combination with midazolam or dexmedetomidine on emotional reactivity, as well as the effects on learning and memory in adult rats at least 48 h after anaesthesia. The evaluation of the potential influence of 100 mg/kg ketamine administered alone and in combination with midazolam (5 mg/kg), or dexmedetomidine (0.25 mg/kg) on spatial learning and recognition memory was studied in adult Wistar rats using the radial maze as well as object recognition and location tests. The influence of these combinations on emotional reactivity was investigated using the new exploration test and the elevated plus maze. Results showed that ketamine alone or in combination with midazolam or dexmedetomidine affected neither spatial and recognition memory, nor emotional reactivity. These results reinforce the safe clinical use of ketamine and its combinations in rats in a research context since the administration of these anaesthetic combinations did not produce significant changes with regard to spatial and recognition memory or emotional reactivity. Furthermore, these results indicate that the quality of scientific data produced in adult rat neurobehavioural research is not jeopardized by the use of these anaesthetic protocols.

Hippocampal long-term potentiation in adult mice after recovery from ketamine anesthesia

Ketamine is frequently used to induce analgesia or anesthesia in laboratory animals, but its effects on learning and memory are poorly characterized. Long-term potentiation (LTP) is considered a cellular mechanism for learning and memory. Ketamine administration immediately abolishes hippocampal LTP in vivo, but whether this effect persists is not known. The authors administered one of two doses of ketamine to adult male C57BL/6 mice and measured LTP in hippocampal slices from the mice 24 h later. Neither LTP induction nor LTP maintenance differed significantly in mice that were administered ketamine compared with mice that were administered saline. The findings suggest that a single intraperitoneal dose of ketamine does not persistently alter LTP in adult male mice.

Neurological disorders in a murine model of chronic renal failure

Cardiovascular disease is highly prevalent in patients with chronic renal failure (CRF). However, data on the impact of CRF on the cerebral circulatory system are scarce—despite the fact that stroke is the third most common cause of cardiovascular death in people with CRF. In the present study, we examined the impact of CRF on behavior (anxiety), recognition and ischemic stroke severity in a well-defined murine model of CRF. We did not observe any significant increases between CRF mice and non-CRF mice in terms of anxiety. In contrast, CRF mice showed lower levels of anxiety in some tests. Recognition was not impaired (vs. controls) after 6 weeks of CRF but was impaired after 10 weeks of CRF. Chronic renal failure enhances the severity of ischemic stroke, as evaluated by the infarct volume size in CRF mice after 34 weeks of CRF. Furthermore, neurological test results in non-CRF mice tended to improve in the days following ischemic stroke, whereas the results in CRF mice tended to worsen. In conclusion, we showed that a murine model of CRF is suitable for evaluating uremic toxicity and the associated neurological disorders. Our data confirm the role of uremic toxicity in the genesis of neurological abnormalities (other than anxiety).